It is possible for a customer facility connected to a multistage switching network to occasionally be blocked from being connected as desired because the network happens to be interconnected in a manner that prevents effecting the desired interconnection. This, of course, is an undesirable situation which, in an appropriately designed network, is remedied by dismantling one or more existing interconnections and rearranging the interconnection paths to accommodate the new request. When such a rearrangement is possible, it is said that the new assignment, which is the new set of interconnections desired to be established, is realizable. A switching network which can realize all possible assignments without rearranging existing connections is said to be nonblocking, while a network which can realize all possible assignments only by occasionally rearranging existing connections is said to be rearrangeable. Typical rearrangeable networks have many fewer crosspoints than their non-blocking counterparts.
U.S. Pat. No. 4,556,007 issued to G. W. Richards on Jan. 21, 1986, discloses a two-stage, rearrangeable multiconnection (broadcast) switching network including an innovative connection arrangement that permanently connects each network input channel to a multiplicity of first stage switch inlets in a predetermined pattern. For any given assignment of input channels to the network output channels connected to a second stage switch, the network can always be arranged such that each input channel is connected by a different first stage switch to the second stage switch and therefore to the output channels which are assigned that input channel. Accordingly, the switching network is a rearrangeable multiconnection network that avoids blocking. The innovative connection pattern advantageously eliminates the need for additional stages of switching thereby reducing both the total number of network crosspoints and the number of crosspoints used to effect each interconnection.
Although the network disclosed in the above-mentioned Richards patent represents an important advance in the art, its reliance on space division switching techniques makes it relatively expensive. In addition, rearrangements in such space division networks sometimes result in open intervals or lost information.
In view of the foregoing, a recognized problem in the art is the expense and reduced communication integrity of known multiconnection networks.